1. Field of the Invention
The present invention relates to a novel flame retardant system for polymers comprising a mixture of two different aryl phosphates, to its preparation, and to its use.
2. Brief Description of the Prior Art
The high combustibility of many polymers means that they have to be provided with flame retardants. One way of increasing the flame retardancy of polymers is to add incombustible or low-combustibility fillers, such as glass, powdered quartz, wollastonite, etc. Another way is to use inorganic flame retardants. Examples which may be mentioned are boron compounds and metal hydroxides. However, large amounts of these types of flame retardants have to be used for adequate flame retardancy. This leads to major problems in the production and processing of polymers.
Use of halogenated compounds is very widespread, examples being tetrabromo-bisphenol A or the corresponding bisepoxide derived therefrom, decabromodiphenyl ether, and brominated polystyrenes. However, the use of halogenated flame retardants is controversial. During combustion corrosive gases such as hydrogen chloride or hydrogen bromide can be produced. There is also a risk that severely toxic dioxin-like products are formed.
U.S. Pat. Nos. 3,689,602, 3,192,242, GB-A-1 487 609 and EP-A-465 605 disclose the use of halogen-containing and also halogen-free phosphates as flame retardants for polymers. However, organophosphorus compounds which are not incorporated into the polymer matrix have plasticizing properties. Large amounts of these phosphorus compounds have to be added in order to achieve effective flame retardancy, and they therefore impair the mechanical and electrical properties of the polymers to an unacceptable degree for many applications.
For example, the strength values and/or the glass transition point are lowered. In addition, some of these compounds are thermally unstable or unstable with respect to hydrolysis. The halogen-containing phosphates are moreover controversial from an environmental point of view, as mentioned above.
It is known that the use of certain aryl thiophosphates or aryl phosphates containing certain functional groups brings about an increase in the flame retardancy of polymers, in particular resins, such as epoxy resins, without substantially impairing their thermal and mechanical properties.
DE-A-44 00 441 has previously disclosed the sole use of the aryl phosphates (termed xe2x80x9caryl phosphate type Ixe2x80x9d hereinafter) containing functional groups. However, there was a need to make further improvement in the use of aryl phosphates as flame retardants for polymers according to DE-A-44 00 441. For example, these aryl phosphates have never been able to pass a fire test to the UL 94 standard. Furthermore, glass transition temperatures above 150xc2x0 C. were generally achieved using a combination of aryl phosphates type I and a further amine hardener. Resins which comprise solely this aryl phosphate generally begin to soften at from 130 to 140xc2x0 C. These temperatures are too low for use in electrical devices or in printed circuits (xe2x80x9cprinted circuit boardsxe2x80x9d). Another disadvantage of DE-A-44 00 441 is that the aryl phosphates described therein discolour the polymers.
An object on which the invention was based was to provide a flame retardant which can be used for polymers and which has at least one of the following properties: high glass transition temperatures and/or markedly less discoloration/yellowing and/or, required for flame retardancy, a very high phosphorus content, the flame retardant being used in polymers and in particular in epoxy resins.
The invention provides a mixture comprising aryl phosphates type I of the general formula (I) 
where
R1 to R4, independently of one another, are hydrogen, alkyl, cycloalkyl, alkenyl, aralkyl or aryl, where the aryl moiety may be unsubstituted or have alkyl substitution,
Y is oxygen or sulphur,
X is OH, SH, COOH, COOR5, NH2, NHR6, NR6R7 or CN,
where R5 to R7, independently of one another, are as defined for R1 to R4, and
n is 0, 1 or 2, and
aryl phosphates type II of the general formula (II) 
where
R8 to R15, independently of one another, are hydrogen, alkyl, cycloalkyl, alkenyl, aralkyl or aryl, where the aryl moiety may be unsubstituted or have alkyl substitution,
m is 0, 1, 2 or 3 and
A is aromatics which contain at least two functional groups.
Particular alkyl radicals R1 to R4 which may be used for the aryl phosphates type I are those having from 1 to 20 carbon atoms, preferably from 1 to 6 carbon atoms, particularly preferably from 1 to 4 carbon atoms. The cycloalkyl radicals preferably have from 5 to 8 ring carbon atoms, in particular 5 or 6 ring carbon atoms, and the alkenyl radical may be linear or branched and contain from 2 to 12 carbon atoms, preferably from 2 to 6 carbon atoms. Preferred aralkyl groups are those containing from 7 to 12 carbon atoms. Preferred aryl radicals used are those with substitution by C1-C4-alkyl radicals and having from 6 to 14 ring carbon atoms. The aryl radicals may also be unsubstituted.
Examples of the radicals R1 to R4 of the aryl phosphates type I are: methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, octyl, dodecyl, tetradecyl, eicosyl, cyclopentyl, cyclohexyl, methylcyclohexyl, vinyl, prop-1-enyl, prop-2-enyl, n-but-3-enyl, n-pent-4-enyl, n-hex-5-enyl, phenyl, naphthyl, biphenyl, benzyl, methylbenzyl, phenylethyl.
The use of these aryl phosphates of type I is particularly preferred when X is NH2, the radicals R1 to R4 are hydrogen and n is 0, 1 or 2.
Particular alkyl radicals R8 to R15 which may be used for the aryl phosphates type II are those having from 1 to 20 carbon atoms, preferably from 1 to 6 carbon atoms, particularly preferably from 1 to 4 carbon atoms. The cycloalkyl radicals preferably have from 5 to 8 ring carbon atoms, in particular 5 or 6 ring carbon atoms, and the alkenyl radical may be linear or branched and contain from 2 to 12 carbon atoms, preferably from 2 to 6 carbon atoms. Preferred aralkyl groups are those containing from 7 to 12 carbon atoms. Preferred aryl radicals used are those with substitution by C1-C4-alkyl radicals and having from 6 to 14 ring carbon atoms. The aryl radicals may also be unsubstituted.
Examples of the radicals R8 to R15 of the above formula are: methyl, ethyl, propyl, isopropyl, n-butyl, isobutyl, tert-butyl, pentyl, hexyl, octyl, dodecyl, tetradecyl, eicosyl, cyclopentyl, cyclohexyl, methylcyclohexyl, vinyl, prop-1-enyl, prop-2-enyl, n-but-3-enyl, n-pent-4-enyl, n-hex-5-enyl, phenyl, naphthyl, biphenyl, benzyl, methylbenzyl, phenylethyl.
The aryl phosphates type II may be unbridged, and here m is preferably 0. The aryl phosphates type II are preferably bridged, m being 1, 2 or 3. Examples of unbridged aryl phosphates type II are triphenyl phosphate and alkylphenyl phosphates.
As A, preference is given to a radical which in the form of A(OH)2 is the compound bisphenol A or resorcinol.
Very particular preference is given to aryl phosphates type II in which R8 to R15 are methyl and A is a radical which in the form of A(OH)2 is bisphenol A.
Some of the compounds are known or may be prepared by known methods. One way of preparing the aryl phosphates type I is transesterification of an appropriate triaryl phosphate with the appropriate phenols in a suitable molar ratio with basic catalysis (Houben-Weyl, Methoden der organischen Chemie [Methods of organic chemistry], Volume 12/2, pp. 371 et seq., Georg Thieme Verlag, Stuttgart, 1964).
Some of the aryl phosphates type II, e.g. diphenyl cresyl phosphate or bisphenol A bis(diphenyl) phosphate, are commercially available products with the trade names Disflamoll DPK(copyright) and Fyrolflex BDP(copyright), respectively, from Bayer or Akzo. Bridged phosphates, e.g. dixylenyl bisphenol A diphosphate (hereinafter xe2x80x9cbisphenol A bis(dixylenylphosphate)xe2x80x9d), may be prepared by bridging of POCl3 with multi-functional aromatics and reaction of suitable phenols. Examples of a preparation are described in EP-A-509 506 and EP-A-764 650.
The mixture preferably comprises amounts of from 3 to 98% by weight, preferably from 13 to 93% by weight, particularly preferably from 25 to 88% by weight, of aryl phosphates type I and amounts of from 2 to 97% by weight, preferably from 7 to 87% by weight, particularly preferably from 12 to 75% by weight, of the aryl phosphates type II, based in each case on the entirety of aryl phosphate type I and aryl phosphate type II. The mixture preferably comprises from 70 to 100% by weight, particularly preferably from 90 to 100% by weight, very particularly preferably from 95 to 100% by weight, of aryl phosphates type I and aryl phosphates type II, based on the mixture.
The invention further provides a process for preparing the inventive aryl phosphate mixture, characterized in that aryl phosphates type I of the general formula (I) 
where R1 to R4, Y, X and n are as defined above, and
aryl phosphates type II of the general formula (II) 
where R8 to R15, A and m are as defined above, are mixed.
The invention further provides a process for preparing polymers provided with flame retardants, characterized in that either the aryl phosphate mixture or the aryl phosphates type I and II is/are separately incorporated into the polymer.
The ideal amounts of the inventive aryl phosphate mixture for the polymer depend on the nature of the polymers and the nature of the aryl phosphates used of type I and II, and may easily be determined by appropriate preliminary experiments. Even very small added amounts of the inventive aryl phosphate mixture are generally effective, meaning that the mixture has practically no effect on the thermal and mechanical properties of the polymers to be rendered flame-retardant.
The inventive aryl phosphate mixture may be used in various physical forms, depending on the type of polymer used and on the desired properties. For example, it may be ground to give a fine-particle form in order to achieve better dispersion in the polymer. Mixtures of the inventive aryl phosphate mixture may also be used. The aryl phosphates of the formula I and aryl phosphates of the formula II may moreover be dissolved in a suitable solvent, e.g. butanone, and this solution may then be added to the polymer.
The amounts of the aryl phosphate mixture usually incorporated into the polymer are from 2 to 80% by weight, preferably from 6 to 60% by weight, particularly preferably from 10 to 50% by weight, based on the polymer. In the case of separate addition, the amounts of aryl phosphate type I incorporated into the polymer are usually from 1 to 50% by weight, preferably from 3 to 40% by weight, particularly preferably from 5 to 35% by weight, and the amounts of the aryl phosphate type II incorporated into the polymer are preferably from 1 to 30% by weight, with preference from 3 to 20% by weight, particularly preferably from 5 to 15% by weight, based on the polymer.
The temperature at which the aryl phosphate mixture or the aryl phosphates type I and II is/are separately incorporated into the polymers is generally from 20 to 200xc2x0 C., preferably from 20 to 80xc2x0 C.
Examples of polymers which may be rendered flame-retardant using the inventive aryl phosphate mixture are:
1. Polyphenylene oxides and polyphenylene sulphides, and also mixtures of these polymers with polystyrene graft polymers or with styrene copolymers such as high-impact polystyrene or with EPDM copolymers or with rubbers, and also mixtures of polyphenylene oxides with polyamides and polyesters.
2. Polyurethanes derived from polyethers, from polyesters or from polybutadiene with terminal hydroxy groups on the one hand and from aliphatic or aromatic polyisocyanates on the other hand, including polyisocyanurates and precursors of these.
3. Polyamides and copolyamides derived from diamines and dicarboxylic acids and/or from aminocarboxylic acids or from the corresponding lactams, for example nylon-4, nylon-6, nylon-6/6, nylon-6/10, nylon-11, nylon-12, poly-2,4,4-trimethylhexamethyleneterephthalamide or poly-m-phenyleneiso-phthalamide, and also copolymers of these with polyethers, e.g. with polyethylene glycols, with polypropylene glycols or with polytetramethylene glycols.
4. Polyesters derived from dicarboxylic acids and dialcohols and/or hydroxy-carboxylic acids or the corresponding lactones, e.g. polyethylene tere-phthalate, polybutylene terephthalate, poly-1,4-dimethylolcyclohexane tere-phthalate and polyhydroxybenzoates, and also block copolyether esters derived from polyethers with terminal hydroxy groups.
5. Unsaturated polyesters derived from copolyesters of saturated and unsaturated dicarboxylic acids and polyhydric alcohols and vinyl compounds as cross-linkers.
6. Polystyrene.
7. Graft copolymers of styrene, e.g. styrene on polybutadiene, styrene and acrylonitrile on polybutadiene, styrene and alkyl(meth)acrylates on poly-butadiene, styrene and acrylonitrile on ethylene-propylene-diene terpolymers, styrene and acrylonitrile on acrylate-butadiene copolymers, and also mixtures of these with random copolymers of styrene or xcex1-methylstyrene with dienes or with acrylic acid derivatives, e.g. the styrene terpolymers known as ABS, MBS, or ASA.
8. Polycarbonates.
9. Epoxy resins derived from polyepoxides, e.g. from diepoxides, in particular from bisphenol A diepoxides, or from cycloaliphatic diepoxides.
10. Phenolic resins and melamine resins and blends of these.
The polymers provided with the inventive aryl phosphate mixtures may also comprise other conventional additives, e.g. heat stabilizers, light stabilizers, UV absorbers, antioxidants, antistats, preservatives, coupling agents, fillers, pigments, lubricants, foaming agents, fungicides, plasticizers, processing aids, other flame-retardant additives and agents to reduce smoke generation. Examples of other flame-retardant additives which may be used are phosphorus-containing salts, e.g. ammonium polyphosphates, melamine and melamine salts, antimony trioxide, aluminium hydroxide, bismuth phosphate, molybdenum oxide, and mixtures of these compounds with zinc oxide and/or with magnesium oxide, or with zinc salts and/or with magnesium oxide salts.
In one preferred embodiment of the process for preparing polymers provided with flame retardant, the polymer is an epoxy resin. Particular preference is given to epoxy resins such as bisphenol A epoxy resins, bisphenol F epoxy resins, phenol novolac epoxy resins, and cresol novolac epoxy resins (see, for example, Houben-Weyl, Methoden der organischen Chemie [Methods of organic chemistry], Vol. E 20/3, pp 1891 et seq., Georg Thieme Verlag, Stuttgart N.Y., 1987).
Advantages of the inventive aryl phosphate mixture for providing flame retardancy to, for example, epoxy resins are that it is possible to achieve the high phosphorus content required for flame retardancy in the moulding composition, yellowing of the moulding composition after curing is lessened, and that they can be used, alone or together with conventional hardeners, for epoxy resins.
Although use may be made of any of the known hardeners for epoxy resins, preference is given to anhydride hardeners and amine hardeners, as described, for example, in Houben-Weyl, Methoden der organischen Chemie [Methods of organic chemistry], Vol. E 20/3, pp 1950 et seq., Georg Thieme Verlag, Stuttgart N.Y., 1987. Examples of anhydride hardeners are: phthalic anhydride, hexahydrophthalic anhydride, methyltetrahydrophthalic anhydride, ethylhexahydrophthalic anhydride and methylnadic anhydride. Suitable amine hardeners are dicyandiamide, 4,4xe2x80x2-diaminodiphenylmethane, 4,4xe2x80x2-diaminodiphenyl sulphone, or BF3 monoethylamine complex. If the inventive aryl phosphate mixtures are used together with the abovementioned conventional hardeners, it is then preferable that the hardener mixtures to be added to the epoxy resins comprise from 10 to 100% by weight, particularly preferably from 50 to 100% by weight, of the inventive aryl phosphate mixture and from 0 to 90% by weight, particularly preferably from 0 to 50% by weight, of one of the anhydride hardeners and/or amine hardeners mentioned, where the total of the % by weight of the aryl phosphate mixture and the anhydride and/or amine hardener has to be 100% by weight.
Polymers provided with flame retardants are usually prepared by reacting liquid or soluble polymers, in particular epoxy resins, with the aryl phosphate mixture and, where appropriate, with the appropriate parts by weight of other hardeners or hardener mixtures, and of other additives (see Table 1, for example), e.g. a solution of dicyandiamide at 10% strength by weight in DMF/methoxypropyl acetate (1:1) and a solution of methylimidazole at 20% strength by weight in methanol. For this, the resin preferably forms an initial charge, and suitable solvents are used, if required, to lower its viscosity and increase its ability to dissolve the additives. The method is generally to add all of the additives and homogenize the mixture with stirring and, if required, with warming to from about 20 to 70xc2x0. This mixture is then generally degassed and freed from excess solvent with stirring for from 5 to 10 minutes at from 20 to 100xc2x0 C., preferably from 40 to 80xc2x0 C. Curing then usually takes place for from about 1 to 4 hours at temperatures of from 60 to 160xc2x0 C., preferably from 80 to 120xc2x0 C., particularly preferably 100xc2x0 C. and for from about 1 to 2 hours at temperatures of from 140 to 200xc2x0 C., preferably from 160 to 190xc2x0 C., particularly preferably at 180xc2x0 C. All the operations may take place in small flat aluminium weighing dishes, for example.
The inventive aryl phosphate mixture may also be used to form a flame-retardant prepolymer. For this, the inventive aryl phosphate mixture is incorporated at a substoichiometric level into a polymer containing reactive groups, in particular epoxy and/or isocyanate groups. The term substoichiometric refers here to the aryl phosphate of type I of the mixture. The resultant prepolymer therefore has incomplete curing and is a flame-retardant prepolymer which can be used and cured. This prepolymer has the advantage of application-related properties which give it improved handling.
There is no need here for separate purchasing, storage and handling by the processor of a flame retardant which may require specific technical measures or measures related to workplace health and safety.
The inventive aryl phosphate mixture may moreover be incorporated into the polymers in such a way as to form what is known as a flame-retardant prepolymer. For this, the inventive aryl phosphate mixture is incorporated at a substoichiometric level into the polymer, with the result that the polymer bears reactive groups, such as epoxy groups or isocyanate groups, not all of which have reacted with the aryl phosphate type I, and which therefore remain available for complete curing.
The preparation of the aryl phosphate mixture and its incorporation into polymers, in particular epoxy resins, may take place continuously or batchwise.
The invention further relates to the use of the aryl phosphate mixtures as flame retardants for polymers. An epoxy resin may be used as polymer.
The epoxy resin compositions provided with the inventive aryl phosphate mixtures may in particular be used as casting and laminating resins for potting compositions and for printed circuit boards in the electronics sector.
The invention further provides a polymer compound obtainable by reacting polymers, in particular epoxy resins, with the inventive aryl phosphate mixture or separately with an aryl phosphate of the formula I and with an aryl phosphate of the formula II.
The invention further provides a polymer comprising the inventive aryl phosphate mixture.
The examples below provide further description of the invention: